Display Device and Manufacturing Method Thereof

ABSTRACT

In a display device using an organic light emitting diode (OLED), the occurrence of a dark spot and peeling of a cathode due to moisture are suppressed. An outer edge portion of a sealing substrate (second substrate) ( 102 ) is made to have a convex shape and a gap between the sealing substrate and an element substrate are controlled by means of this convex region. Thus, since it is not required that a layer ( 106 ) having adhesion for bonding together the sealing substrate and the element substrate has a function for controlling the gap, the thickness of the layer can be minimized. Therefore, the amount of moisture which is transmitted through the layer (having adhesion) made of an organic material and penetrated in a sealed region can be reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/821,927, filed Apr. 12, 2004, now pending, which is a divisional ofU.S. application Ser. No. 10/062,294, filed Jan. 31, 2002, now U.S. Pat.No. 6,724,150, which claims the benefit of a foreign priorityapplication filed in Japan as Serial No. 2001-026176 on Feb. 1, 2001,all of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device using an organic lightemitting element and a manufacturing method thereof, and moreparticularly to a display device using an organic light emitting elementcapable of keeping a stable light emitting property for a long period.

Note that the organic light emitting element in this specificationindicates an element in which an organic compound layer is sandwichedbetween two electrodes to produce light emission. As the organic lightemitting element, there is a light emitting element using an organiclight emitting diode (OLED). The organic light emitting diode is aphosphor in which an organic compound layer is sandwiched between twoelectrodes, and a hole is injected from one electrode and an electron isinjected from the other electrode so that the hole and the electron arecombined in the organic compound layer to thereby produce lightemission.

2. Description of the Related Art

Recently, a display device using an organic light emitting element isactively researched. In the case of the display device using the organiclight emitting element, greater reduction in its weight and thickness ispossible as compared with a conventional CRT and an application tovarious uses is being progressed. Since it is now possible to connect amobile telephone, a personal digital assistant (PDA), or the like withthe Internet, the amount of information to be displayed has dramaticallyincreased, and the need for color display and high resolution of adisplay device is increased.

On the other hand, it is important for a display device incorporated insuch a personal digital assistant to be reduced in its weight. Forexample, in the case of the mobile telephone, a product which weighsless than 70 g is currently on the market. For weight reduction, areview of most of parts to be used such as individual electronic parts,a case, and a battery is being conducted. However, in order to realizefurther weight reduction, it is also necessary to promote weightreduction of a display device.

A display device in which a pixel portion is composed of an organiclight emitting element is of a self light emission type and does notrequire a light source such as a back light used in a liquid crystaldisplay device. Thus, it is being greatly promised as means forrealizing reduced weight and thickness.

With the organic light emitting element, blue color light emission ispossible and a self light emission display device capable of full colordisplay can be realized. However, in the organic light emitting element,various deterioration phenomena are recognized, which hinder thepractical use. Thus, it is considered necessary to solve such a problemas soon as possible.

For example, a dark spot is a point defect of non-light emission, whichis observed in a pixel portion, and is recognized as a problem formarkedly degrading display quality. It is said that the dark spot is aprogress type defect which increases even without operating the element,if moisture is present. It is considered that the dark spot is caused byan oxidation reaction of a cathode made of alkali metal.

Therefore, the display device using the organic light emitting elementis constructed such that an element substrate on which a light emittingelement is provided and a sealing substrate which is provided so as tooppose the element substrate are bonded together through a seal memberhaving adhesion so that the light emitting element is not exposed tooutside air including moisture. The sealing substrate is made ofstainless steel or metal such as aluminum, which is easy to process. Adry agent is disposed in a concaved portion of the surface of thesealing substrate.

The seal member is mixed with a filler to control a gap between theelement substrate and the sealing substrate. Thus, the seal member hasboth a function for bonding together the sealing substrate and theelement substrate and a function for controlling the gap between thesealing substrate and the element substrate. Therefore, when the gapbetween the element substrate and the sealing substrate is set to be ageneral value of 10 μm to 50 μm, it is necessary to change the thicknessof the seal member in accordance with the size of the gap.

Note that the shortest distance between the light emitting element and asurface of the sealing substrate opposing the light emitting element iscalled a gap between the sealing substrate and the element substrate, orsimply a gap.

Now, the seal member for controlling the gap between the elementsubstrate and the sealing substrate is made of an organic resin materialand has higher moisture permeability than an inorganic material such asa glass material. For example, at a temperature of 60° C. and a humidityof 90%, moisture permeability becomes 15 g/m²·24 hr. to 30 g/m²·24 hr.Even when the sealing substrate and the element substrate are sealedwith the seal member, the organic light emitting element is deterioratedby a water vapor which is transmitted through the seal member andpenetrated in a sealed region. The amount of water vapor to betransmitted through the seal member is determined by the product of anarea of the seal member to be exposed to outside air and moisturepermeability. Thus, it is desirable that the area of the seal member tobe exposed to outside air is small. That is, it is desirable that thethickness of the seal member is minimized.

As the thickness of the seal member is increased, the amount of moistureto be transmitted through the seal member is increased. Even if the dryagent is provided, the light emitting element is deteriorated by themoisture which is not absorbed by the dry agent. That is, an object ofthe present invention is to reduce the amount of moisture to betransmitted through the seal member.

Also, a method of thinning a glass substrate may be conceived to achieveweight reduction of the personal digital assistant. However, the glasssubstrate is more likely to break as it becomes thinner and its shockresistance is reduced. In particular, when the sealing substrate made ofmetal and the element substrate made of glass are bonded together,because of a difference in thermal expansion coefficient, a distortionis caused due to a sudden change in a temperature and a crack is causedin the substrate made of glass. However, this becomes a critical defectin the case where such a substrate is used for the personal digitalassistant.

Therefore, an object of the present invention, is to prevent thebreaking of the substrate to improve the durability thereof in the caseof a construction in which the glass substrate is reduced in thicknessto realize a thin display device.

Thus, although the display device composed of the organic light emittingelement is very effective for weight reduction of a display device,there remain problems to be solved in order to ensure the reliability ofthe organic light emitting element.

SUMMARY OF THE INVENTION

The present invention relates to a technique for solving such problemsand an object of the present invention is to provide a display deviceusing an organic light emitting element having high reliability and amanufacturing method thereof.

As the substrate made of glass has become thinner, when the elementsubstrate made of glass and the sealing substrate made of metal arebonded together, because of a difference in a thermal expansioncoefficient, the possibility that the element substrate made of glass isbroken due to a sudden change in a temperature becomes high. In order toprevent this, according to the present invention, a substrate made ofglass is used for the element substrate and the sealing substrate toobtain an identical thermal expansion coefficient. Thus, resistancethereof against a sudden change in a temperature is increased, and thusthe object of the present invention is attained.

Further, according to the present invention, the surface of the sealingsubstrate made of glass is processed to have a concaved portion and adry agent is disposed in the concave portion. Thus, as a conventionalcase, the dray agent can be provided in a sealed space surrounded by theelement substrate, the sealing substrate, and the seal member to capturemoisture which is transmitted through an adhesion member and penetratedin the sealed space. Calcium oxide, barium oxide, or the like can besuitably used for the dry agent. The dry agent may be provided on, forexample, a driver circuit. Then, since the dry agent is present close tothe light emitting element in a sealed region between the elementsubstrate and the sealing substrate, penetration of moisture to thelight emitting element can be reduced. Thus, stability of the lightemitting element can be improved. For example, a dark spot caused byoxidation of a cathode can be reduced.

Also, according to the present invention, the sealing substrate made ofglass is processed so that an outer edge portion of the sealingsubstrate protrudes in a convex shape. The gap between the elementsubstrate and the sealing substrate is controlled by the convex portion.Then, since a layer having adhesion which is provided between theelement substrate and the scaling substrate is required to have only afunction for bonding the element substrate and the sealing substratetogether, a function for controlling the gap becomes unnecessary. Thus,the thickness of the layer having adhesion can be made as small aspossible as its material permits. Therefore, the amount of moisturewhich is transmitted through the layer having adhesion and penetrated inthe sealed region can be reduced, whereby an object of the presentinvention, that is, reduction of the amount of moisture transmittedthrough the layer having adhesion, is attained. It is desirable that thethickness of the layer having adhesion (adhesion member) is 10 μm orless, preferably, 1 μm or less.

An abrasive machining method (sandblast method) can be used as a methodof processing the surface of the sealing substrate. The abrasivemachining method is a technique of blasting sands, fine steel billetsand the like with compressed air to process the surface of a substratemade of glass.

One example of the construction of the present invention will bedescribed using FIGS. 8A to 8C. FIGS. 8A to 8C are cross sectional viewsof a display device using an organic light emitting device of thepresent invention.

FIG. 8A shows an example where, in a display device constructed bybonding together an element substrate and a sealing substrate through alayer having adhesion, the surface of the sealing substrate is processedand a dry agent and a permeable film are provided in a sealed region. Afirst substrate 101 and a second substrate 102 are made from atranslucent substrate, for example, a glass substrate. The firstsubstrate is the element substrate on which an organic light emittingelement is provided in a display region 129. The second substrate is thesealing substrate, and the surface thereof is recessed by processing. Adry agent 107 and a permeable film are disposed thereon. Note that, whenlight emitted from the organic light emitting element is picked up fromthe sealing substrate side, it is desirable the dry agent and thepermeable film be provided outside the display region.

Note that, in the present invention, a region of the second substratelocated on the same plane as a portion in which a layer 106 havingadhesion is bonded to the second substrate is a first region 103 of thesecond substrate. Also, a region which is concaved relative to the firstregion is a second region 104. Further, a region which is concavedrelative to the second region is a third region 105. In other words,when a surface of the second substrate opposing the organic lightemitting element is taken as the front surface and it is viewed from therear surface of the second substrate, the first region is protruded in aconvex shape relative to the second region and the third region.

The dry agent 107 is provided in the third region 105. A granularmaterial or a flat sheet material can be also used for the day agent.For filling the dry agent, it is preferable that the third region isrecessed by 50 μm to 150 μm relative to the second region.

The permeable film having high moisture permeability and having watervapor permeability is composed of an adhesive layer 125, a porous layer126, and a base member 127. In order to contain the dry agent in thethird region, the permeable film is attached with the adhesive layer 125contacting with a part of the second region. The permeable film composedof the adhesive layer, the porous layer, and the base member, has athickness of 150 μm to 300 μm. Also, it is desirable that the firstsubstrate is located at a distance 10 μm to 50 μm or more apart from thesurface of the base member constituting the permeable film so that thepermeable film is not in contact with the first substrate. Thus, it isdesirable that the second region is recessed by 160 μm to 350 μmrelative to the first region.

Both an ultraviolet light curable resin and a heat curable resin can beused as the layer 106 having adhesion for bonding the element substrateand the sealing substrate together. The amount of moisture entering intothe sealed region is determined by the product of an area of the layerhaving adhesion which is exposed to outside air and moisturepermeability. Thus, it is desirable that the thickness of the layerhaving adhesion is minimized to reduce the area exposed to outside air.

According to the present invention, since the outer edge portion (firstregion) of the second substrate is protruded in a convex shape, the gapbetween the first substrate and the second substrate can be determinedby the height of the convex portion of the outer edge portion of thesecond substrate. The layer having adhesion is not required to have afunction for controlling the gap and thus may be used only to facilitatebonding of the first substrate and the second substrate. Thus, the layerhaving adhesion can be made as thin as possible insofar as its materialpermits.

Next, another example of the present invention is indicated. The presentinvention described below adopts a construction which takes intoconsideration not only the reduction of moisture which is transmittedand enters through the layer having adhesion but also the reduction ofthe amount of moisture left in a dry gas in the sealed region.

FIG. 8B is a cross sectional view of an organic light emitting element.When compared with FIG. 8A, a difference from FIG. 8 is that the gapbetween the first substrate and the second substrate is made smaller at10 urn to 50 urn in the display region 129. The permeable film has athickness of 150 μm to 300 μm and the gap having such a large thicknessis unnecessary in the display region in which the permeable film is notprovided. When the gap in the display region which takes up apredominantly large area of a display device is reduced to 3% to 50% ascompared with that in FIG. 8A, a volume of a sealed space, that is, avolume of the dry gas is reduced, and the total amount of moisture leftin the gas is reduced as a result.

FIG. 8C shows an example in which a flat sheet dry agent 107 is disposedin the third region 105 of the second substrate 102. Calcium oxide orthe like is preferably used for the flat sheet dry agent.

In order to prevent mixing of fine powder into the display region whichoccurs when the dry agent is partially peeled off or otherwise damageddue to a shock applied thereon, adhesives 109 are provided in severallocations on the surface of the dry agent and a porous film 108 having athickness of 10 μm to 30 μm is attached to the dry agent through theadhesives 109. Thus, when the dry agent is covered with the porous film,fine powder produced due to a mechanical shock can be contained insidethe porous film. It is preferable that the porous film are hollowed in acircular shape in two or more locations to expose the dry agent, anadhesive 110 is applied to the thus exposed portions, whereby the dryagent and the second substrate are bonded to each other. The thicknessof the adhesive can be set to be 1 μm to 5 μm by controlling the amountof the adhesive to be applied onto the surface of the dry agent. In thecase of FIG. 8C, it is desirable that a thickness of the porous film, athickness of the dry agent, and a thickness of the adhesive are adjustedso that the dry agent and the porous film can be received in the thirdregion recessed by 50 μm to 150 μm relative to the second region.

In the cases of FIGS. 8A and 8B in order not to crush the permeable filmdue to weight of the dry agent, it is required that the base member 127having a thickness of 100 μm to 150 μm is provided in contact with theporous film 126 having a thickness of about 10 μm to 70 μm. Thus, thethickness of the base member and the thickness of the porous film needsto be increased to improve a mechanical strength of the permeable film.Further, since the adhesive layer 125 having a thickness of 40 μm to 80μm is required for adhering the film to the substrate, the overallthickness of the permeable film becomes as large as 150 μm to 300 μm.Thus, the amount of moisture left in the gas in the sealed space isincreased in correspondence with a volume occupied by the permeablefilm.

However, in the case of FIG. 8C, the film is only required to cover thedry agent and needs not to have high mechanical strength. Thus, evenwhen a thin porous film having a thickness of 10 μm to 30 μm is used,there is no problem for practical use. Also, a volume of the sealedspace can be reduced due to the reduced thickness of the film. To coverthe dry agent, the porous films are provided on an upper surface(surface opposing the second substrate) of the dry agent and on a lowersurface (surface opposing the first substrate) thereof. Thus, when theporous film having a thickness of 10 μm to 30 μm is used, the thicknessof the porous film within the gap becomes twice as large, that is, 20 μmto 60 μm. Even so, the thickness of the porous film within the gap ismade smaller than the thickness of permeable film. If the amount of dryagent is the same, a volume of the sealed region can be reduced with theconstruction shown in FIG. 8C, and thus the amount of moisture left inthe gas becomes small. This leads to the suppression of oxidationreaction of the cathode due to moisture and the useful life of thedisplay device can be increased.

Note that, in the case of FIG. 8C, it is preferable that the secondregion 104 is recessed by 10 μm to 50 μm relative to the first region sothat the gap between the first substrate and the second substrate in thedisplay region is set to be 10 μm to 50 μm.

Also, in the present invention, since the sealing substrate and theelement substrate are translucent, light emitted from the organic lightemitting element provided on the element substrate may be emitted towardeither the sealing substrate side or the element substrate side. Thiscan be freely designed in consideration of a size of the light emissionarea of the organic light emitting element and the like.

The present invention based on the above descriptions is as follows.

According to a first aspect of the present invention described in thisspecification, there is provided a display device comprising a firstsubstrate on which an organic light emitting element is provided and asecond substrate which is translucent, the first substrate and thesecond substrate being bonded together through a layer having adhesion,characterized in that a surface of the second substrate opposing thefirst substrate includes to a first region and a second region, thefirst region is adhered with the layer having adhesion, and the secondregion is located inside the first region and is concaved relative tothe first region.

In the first aspect of the present invention described in thisspecification, a portion of the sealing substrate to which the layerhaving adhesion is provided is made convex to the element substrate.Thus, a gap between the first substrate and the second substrate can bedetermined by a convex portion of the second substrate and the layerhaving adhesion can be used only for the purpose of bonding the firstsubstrate and the second substrate together.

According to a second aspect of the present invention described in thisspecification, there is provided a display device comprising a firstsubstrate on which an organic light emitting element is provided and asecond substrate which is translucent, the first substrate and thesecond substrate being bonded together through a layer having adhesion,characterized in that: a surface of the second substrate opposing thefirst substrate includes a first region, a second region, and a thirdregion; the first region is adhered with the layer having adhesion; thesecond region is located inside the first region and concaved relativeto the first region; the third region is located inside the secondregion and concaved relative to the second region; and a dry agent isprovided in the third region.

In the second aspect of the present invention described in thisspecification, since a portion of the second substrate to which thelayer having adhesion is adhered is convex, the sealing substrate has afunction for controlling the gap, as in the first aspect of the presentinvention described in this specification. Further, the dry agent isprovided in a concaved portion of the surface of the second substrate tocapture moisture penetrated in the sealed region. Thus, the stability ofthe organic light emitting element is ensured for driving over a longperiod of time.

According to a third aspect of the present invention described in thisspecification, there is provided a display device characterized in that,in the second aspect of the present invention described in thisspecification, a permeable film is adhered to a part of the secondregion so that the dry agent is contained in the third region.

As in the case of the third aspect of the present invention described inthis specification, a permeable film may be used as means for providingthe dry agent in the third region.

According to a fourth aspect of the present invention described in thisspecification, there is provided a display device comprising a firstsubstrate on which an organic light emitting element is provided, alayer having adhesion for enclosing with a gap an area surrounding aregion in which the organic light emitting element is provided on thefirst substrate, and a second substrate which is translucent, the firstsubstrate and the second substrate being bonded together through thelayer having adhesion, characterized in that: a surface of the secondsubstrate opposing the first substrate includes a first region, a secondregion, and a third region: the first region is adhered with the layerhaving adhesion: the second region is surrounded by the first region andconcaved relative to the first region: the third region is locatedbetween the layer having adhesion and an upper portion of the region inwhich the organic light emitting element is provided and is concavedrelative to the second region; and a dry agent is located in the thirdregion.

In the fourth aspect of the present invention, a difference from thesecond aspect of the present invention described in this specificationis that the dry agent is provided only in a region outside the displayregion.

According to a fifth aspect of the present invention described in thisspecification, there is provided a display device characterized in that,in the fourth aspect of the present invention described in thisspecification, a permeable film is provided between the layer havingadhesion and the upper portion of the region in which the organic lightemitting element is provided, and the permeable film is adhered to apart of the second region to thereby contain the dry agent in the thirdregion.

As in the case of the fifth aspect of the present invention described inthis specification, a permeable film may be used as means for providingthe dry agent in the third region. The permeable film is preferablydisposed outside the display region.

According to a sixth aspect of the present invention described in thisspecification, there is provided a display device characterized in that,in the third or the fifth aspect, the permeable film adhered to thesecond region is fit between a plane which is contact with the firstregion and a surface on which the permeable film is adhered to thesecond region. In other words, it is required that the permeable film isat least not in contact with the first substrate.

According to a seven aspect of the present invention described in thisspecification, there is provided a display device characterized in that,in the second aspect of the present invention described in thisspecification or in the fourth aspect of the present invention describedin this specification, a difference in height between a bottom portionof the second region which is concaved relative to the first region andthe first region is 10 μm to 50 μm. One example of the seven aspect ofthe present invention described in this specification has been describedalready using FIG. 8C.

According to an eighth aspect of the present invention described in thisspecification, there is provided a display device characterized in that,in the third aspect of the present invention described in thisspecification or in the fifth aspect of the present invention describedin this specification, a difference in height between a bottom portionof the second region which is concaved relative to the first region andthe first region is 160 μm to 350 μm. One example of the eight aspect ofthe present invention has been described already using FIGS. 8A and 8B.

According to a ninth aspect of the present invention described in thisspecification, there is provided a display device characterized in that,in any one of the first through eighth aspects of the present inventiondescribed in this specification, a difference in height between a bottomportion of the third region which is concaved relative to the secondregion and the second region is 50 μm to 150 μm. One example of theninth aspect of the present invention described in this specificationhas been described already using FIGS. 8A to 8C.

According to a tenth aspect of the present invention described in thisspecification, there is provided a display device characterized in that,in any one of the first through ninth aspects of the present inventiondescribed in this specification, the first substrate is a glasssubstrate.

According to an eleventh aspect of the present invention described inthis specification, there is provided a display device characterized inthat, in any one of the first through ninth aspects of the presentinvention described in this specification, each of the first substrateand the second substrate is a glass substrate.

The shock resistance of the substrate decreases as it becomes thinner.Thus, when substrates are made from different materials, a crack iscaused in a substrate made of glass due to a sudden change in atemperature. This is a phenomenon resulting from a difference in thermalexpansion coefficient. However, when the first substrate and the secondsubstrate are made of the same material as in the case of the eighthaspect, occurrence of a crack due to a thermal shock can be prevented.

According to a twelfth aspect of the present invention described in thisspecification, there is provided a display device characterized in that,in any one of the first through eleventh aspects of the presentinvention described in this specification, a thickness of the layerhaving adhesion is 10 μm or less.

According to the present invention, since it is unnecessary to keep thegap by the layer having adhesion, the thickness of the layer havingadhesion can be minimized. It is particularly desirable that thethickness of the layer having adhesion be set to 10 μm or less in orderto suppress the penetration of moisture in the sealed region.

According to a thirteenth aspect of the present invention described inthis specification, there is provided a method of manufacturing adisplay device in which a first substrate and a second substrate whichare translucent are bonded together through a layer having adhesion andan organic light emitting element is provided in the first substrate,characterized by comprising: a first step of setting a region of thesecond substrate to which the layer having adhesion is adhered as afirst region and providing a first mask in at least the first region; asecond step of digging the second substrate by an abrasive machiningmethod to form a second region which is concaved relative to the firstregion: a third step of removing the first mask: a fourth step ofproviding a second mask in a region of the second substrate in which alleast the first mask was provided and a region located above a region inwhich the organic light emitting element is provided and digging thesecond substrate by an abrasive machining method to thereby form a thirdregion which is concaved relative to the second region; and a fifth stepof providing a dry agent in the third region.

According to a fourteenth aspect of the present invention described inthis specification, there is provided a method of manufacturing adisplay device characterized by further including, in the thirteenthaspect of the present invention described in this specification, a sixthstep of providing a permeable film in the second region after the fifthstep.

As a method of providing the dry agent in the third region, there are amethod of adhering the dry agent to the second substrate and a method ofadhering an adhesive layer of the permeable film to the second region tothereby contain the dry agent in the third region. The fourteenth aspectof the present invention described in this specification is a methodused for the latter method.

According to a fifteenth aspect of the present invention described inthis specification, there is provided a method of manufacturing adisplay device characterized in that, in the fourteenth aspect of thepresent invention described in this specification, a digging depth ofthe second substrate in the second step is larger than a thickness ofthe permeable film

According to a sixteenth aspect of the present invention described inthis specification, there is provided a method of manufacturing adisplay device characterized in that, in the thirteenth aspect of thepresent invention described in this specification, the digging depth inthe second step is 10 μm to 50 μm. According to the sixteenth aspect ofthe present invention described in this specification, by processing thesurface of the second substrate in the structure shown in FIG. 8C, forexample, the second region can be recessed by 10 μm to 50 μm relative tothe first region.

According to a seventeenth aspect of the present invention described inthis specification, there is provided a method of manufacturing adisplay device characterized in that, in the fourteenth or the fifteenthaspect of the present invention described in this specification, thedigging depth in the second step is 160 μm to 350 μm. According to theseventeenth aspect of the present invention described in thisspecification, in the structure shown in FIG. 8A or 8B, the secondregion 104 can be recessed by 160 μm to 350 μm relative to the firstregion 103.

According to an eighteenth aspect of the present invention described inthis specification, there is provided a method of manufacturing adisplay device characterized in that, in any one of the thirteenththrough seventeenth aspects of the present invention described in thisspecification, the digging depth in the third step is 50 μm to 150 μm.According to the eighteenth aspect of the present invention described inthis specification, as shown in FIGS. 8A to 8C, the third region 105 inwhich the dry agent is provided can be recessed by 50 μm to 150 μmrelative to the first region 104.

According to a nineteenth aspect of the present invention described inthis specification, there is provided a method of manufacturing adisplay device characterized by further including, after the fifth stepin the thirteenth through sixteenth aspect of the present inventiondescribed in this specification, a sixth step of bonding the firstsubstrate and the second substrate together through the layer havingadhesion and a seventh step of cutting the first substrate and thesecond substrate by a gas laser.

According to a twentieth aspect of the present invention described inthis specification, there is provided a method of manufacturing adisplay device characterized by further including, after the sixth stepin any one of the fourteenth through sixteenth aspects of the presentinvention described in this specification, a seventh step of bonding thefirst substrate and the second substrate together through the layerhaving adhesion and an eighth step of cutting the first substrate andthe second substrate by a gas laser.

According to a twenty-first aspect of the present invention described inthis specification, there is provided a method of manufacturing adisplay device characterized in that, in the nineteenth or twentiethaspect of the present invention described in this specification, the gaslaser is a CO₂ laser.

In accordance with another aspect of the present invention, a lightemitting device of the present invention includes a first substrate anda second substrate opposed to each other and at least a light emittinglayer interposed therebetween where the light is emitted out from thelight emitting device through the second substrate and an inner surfaceof the second substrate is provided with minute unevennesses in orderthat outside light is prevented from reflecting at the interface betweenthe second substrate and a sealed space and in an interface between thesecond substrate and air. Further, the heights of the minuteunevennesses are set to be 0.1 μm to 3 μm, preferably, 0.1 μm to 0.5 μm.In order to prevent diffraction, it is preferable that the unevennesseshaving different curvatures are provided to improve scattering property.Taking the spacing (pitch) between the convex portions as X, it ispreferable to set X=0.05 to 1 μm (more preferably between 0.3 and 0.8μm). In other words, by setting the pitch of the convex portions to benearly equal to the wavelength of visible light, diffuse reflection(irregular reflection) of the reflected light can be made to occureffectively.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a cross sectional view of a display device using an organiclight emitting element according to Embodiment Mode 1;

FIG. 2 is a cross sectional view of a display device using an organiclight emitting element according to Embodiment Mode 2;

FIG. 3 is a cross sectional view of a display device using an organiclight emitting element according to Embodiment Mode 3;

FIG. 4 is a cross sectional view of a display device using an organiclight emitting element according to Embodiment 1;

FIG. 5 is a top view for explaining a structure of a pixel portion ofthe display device using the organic light emitting element according toEmbodiment 1;

FIG. 6 shows an equivalent circuit of the pixel portion of the displaydevice using the organic light emitting element according to Embodiment1;

FIGS. 7A to 7D are cross sectional views indicating a method ofmanufacturing a sealing substrate in Embodiment Mode 1;

FIGS. 8A to 8C are cross sectional views of a display device using anorganic light emitting element according to the present invention;

FIG. 9 is a perspective view indicating a method of cutting a glasssubstrate using a CO₂ laser;

FIGS. 10A to 10D are explanatory views of examples of electronicappliances; and

FIGS. 11A to 11C are explanatory views of examples of electronicappliances.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode 1

An embodiment mode of the present invention will be described usingFIG. 1. FIG. 1 is a cross sectional view of an active matrix displaydevice using an organic light emitting element.

A driver circuit portion 111 and a pixel portion 112 which are composedof TFTs are formed on a first substrate (element substrate) 101.

Substrates made of glass such as barium borosilicate glass,aluminoborosilicate glass, or quartz glass are used as the firstsubstrate and the second substrate (sealing substrate) 102.

The surface of the second substrate is processed by an abrasivemachining method and selectively shaved. By this processing, the surfaceof the second substrate has a first region 103, a second region 104, anda third region 105. The first region is a surface to which a layerhaving adhesion is adhered. When viewed from a rear surface of thesecond substrate, the first region is protruded in a convex shaperelative to the second region and the third region.

An epoxy system adhesive is used for a layer 106 having adhesion. It isdesirable that the thickness of the layer having adhesion be as small aspossible. LIXSON BOND LX-0001 sold by Chisso Corporation can be alsoused as the adhesive. LX-0001 is a two-part epoxy resin. After LX-0001is applied onto the first substrate, while the first substrate and thesecond substrate are pressed, it is cured at 100° C. for 2 hours. Athickness of the adhesive after the curing becomes 0.5 μm to 2.0 μm.

A dry agent 107 is provided in a concave portion of the third region.Calcium oxide is used for the dry agent. A known material can be usedfor the dry agent. In this embodiment mode, a planer dry agent is used.A thickness of the dry agent is desirably 10 μm to 80 μm. In thisembodiment mode, the thickness of the dry agent is set to be 80 μm. Thedry agent absorbs moisture entering into an organic light emittingelement after the first substrate and the second substrate are sealedthrough the layer having adhesion. Since the dry agent is providedadjacent to a region in which the light emitting element is provided, aconcentration of moisture in a sealed region can be reduced and a lifeof the display device can be extended.

In order to avoid moving of fine powder of the dry agent into the pixelportion and the drive circuit portion, a porous film 108 is provided soas to cover the dry agent. An adhesive 109 is applied in dots onto thesurface of the dry agent and the porous film is adhered to the dryagent. Also, the porous film is cut out in a circle and an adhesive 110is applied to the thus exposed portion of the dry agent to thereby bondthe dry agent 107 and the second substrate 102 with each other.

It is desirable that the porous film be as thin as possible. In thisembodiment mode, the thickness of the porous film is set to be 10 μm.Also, the thickness of the adhesive can be set to be 5 μm or less,preferably, 1 μm or less by controlling the amount thereof to be appliedto the dry agent. In this embodiment mode, the thickness of the adhesiveis set to be 5.0 μm. Since the thickness of the dry agent is 80 μm, whenthe third region is recessed by about 110 μm relative to the secondregion, the dry agent 107, the adhesives 109 and 110, and the porousfilm 108 can be received in the third region.

In the pixel portion, the gap between the first substrate and the secondsubstrate is preferably set to be 10 μm to 50 μm. In order to set thegap in the pixel portion to be within this range, the second region 104is preferably recessed by about 10 μm to 50 μm relative to the firstregion 103. In this embodiment mode, in order to set the gap between thefirst substrate and the second substrate to be 50 μm in the pixelportion, the second region is recessed by 48 μm relative to the firstregion. This is a value which is obtained by considering the thickness(2 μm) of the layer having adhesion in this embodiment mode. Note that,with respect to the gap between the organic light emitting element andthe sealing substrate in the pixel portion, a difference of several μmis actually produced due to the thickness of an interlayer insulatingfilm 121. However, for convenience of description, it is assumed thatthe thickness of the interlayer insulating film can be neglected.

Since there is a gap of about 50 μm between the porous film 108 and thedriver circuit portion, the porous film 108 is not brought into contactwith the driver circuit portion and thus TFTs in the driver circuit arenot damaged.

An organic light emitting element 116 has a structure in which a cathode113, an organic compound layer 114, and an anode 115 are laminated inorder and light emitted from the light emitting element is outputted tothe second substrate 102 side. With such a structure, the cathode madeof a conductive film having a reflective property can be overlaid overan electrode of a TFT and a wiring, a light emitting area is increased,and display having high luminance and good visibility can be obtained.

A material including magnesium (Mg), lithium (Li), or calcium (Ca) whichhas a small work function is used for the cathode 113. Preferably, anelectrode made of MgAg (material in which Mg and Ag are mixed atMg:Ag=10:1) is used. In addition, it is also possible to use an MgAgAlelectrode, an LiAl electrode, and an LiFAl electrode. The cathode ismade of a material such as MgAg or LiF. The thickness of the cathode ispreferably 100 nm to 200 nm.

The anode 115 is made of an ITO (indium tin oxide) film that is atranslucent conductive film. The thickness of the anode is preferably100 nm to 200 nm.

The organic compound layer 114 is obtained by laminating an electrontransport layer, a light emitting layer, a hole transport layer, and ahole injection layer in order. However, the organic compound layer mayalternatively be obtained by laminating an electron transport layer, alight emitting layer, and a hole transport layer or by laminating anelectron injection layer, an electron transport layer, a light emittinglayer, a hole transport layer, and a hole injection layer, in the statedorder. In the present invention, any known structure may be used.

With respect to specific light emitting layers, preferably,cyanopolyphenylene is used for a light emitting layer for emitting lighthaving a red color, polyphenylenevinylene is used for a light emittinglayer for emitting light having a green color, and polyphenylenevinyleneor polyalkylphenylene is used for a light emitting layer for emittinglight having a blue color. The thickness of the light emitting layersmay be set to 30 nm to 150 nm.

The above example is one example of materials which can be used for alight emitting layer, and the materials are not limited to these.Materials for forming a light emitting layer, a hole transport layer, ahole injection layer, an electron transport layer, and an electroninjection layer can be freely selected from possible combinations.

TFTs which compose the driver circuit portion and the pixel portion areprovided on a base film 117 having an insulating property. A TFT iscomposed of a semiconductor film 118, a gate insulating film 119, a gateelectrode 120, an interlayer insulating film 121, a drain electrode 122,and a source electrode 123. Preferably, the thickness of thesemiconductor film is set to be 10 nm to 150 nm, the thickness of thegate insulating film is set to be 50 nm to 200 nm, the thickness of thegate electrode is set to be 50 nm to 8001 nm, the thickness of theinterlayer insulating film is set to be 1 μm to 6 μm, and thethicknesses of the drain electrode and the source electrode are set tobe 200 nm to 800 nm.

In order to prevent a disconnection in the organic compound layer 114and a short circuit between the anode 115 and the cathode 113 due to abreak of the organic light emitting element, a bank 124 made of anorganic resin such as acrylic or polyimide, preferably a photosensitiveorganic resin, is provided so as to partially overlap with end portionsof the cathode. When the organic compound layer is formed along gradualtapers of the bank 124, the disconnection in the organic compound layerin end portions of the cathode and therefore the short circuit betweenthe anode and the cathode resulting from the disconnection in theorganic compound layer is prevented. The film thickness of the bank isset to be 1 μm to 3 μm.

In this embodiment mode, in order to set the gap between the firstsubstrate and the second substrate in the pixel portion to be 50 μm, thenecessary thickness of the layer having adhesion is 2 μm. Thus, an areain side surfaces of the display device in which ihe organic resinmaterial is exposed to outside air is reduced so that the amount ofmoisture transmitted through the organic resin material (layer havingadhesion) can be greatly reduced as compared with a conventional art.

That is, the amount of moisture which is transmitted through the layerhaving adhesion and penetrated in the sealed space can be reduced. Thus,the object of the present invention is attained and the life of theorganic light emitting element can be improved.

FIGS. 7A to 7D are cross sectional views for explaining steps forprocessing a substrate by an abrasive machining method. There is MB-1produced by Sintobrator. Ltd. as one example of an apparatus used forthe above processing.

FIG. 7A is a cross sectional view showing a state in which first masks201 are disposed in selective positions on a substrate 202 made of glassbefore processing. The first mask is disposed in a region in which thelayer having adhesion is provided. First, a film is adhered to thesurface of the substrate, exposed to ultraviolet light, then developedwith an alkalescent solution, and dried to thereby form the first mask.An ultraviolet curable type urethane resin is preferably used for thefilm adhered to the surface of the substrate. This is because of itshigh shock resistance in the abrasive machining process. The thicknessof first mask is preferably 0.05 mm to 0.5 mm.

FIG. 7B is a cross sectional view indicating a first processing step ofperforming abrasive machining by jetting fine powder onto the substrate.Fine powder having an average particle size of 3 μm to 40 μm is jettedonto the surface of the substrate to selectively remove a portion inwhich the first mask is not present. After the processing, the substrateis washed to remove processing scraps on the substrate. Thus, a firstregion 203 and a second region 204 which is recessed relative to thefirst region can be formed onrr the surface of the substrate.

FIG. 7C is a cross sectional view indicating a second processing step ofproviding second masks 206 on the substrate and performing abrasivemachining. Fine powder is jetted to dig the surface of the substrate.Thus, a third region 205 which is recessed relative to the second regioncan be formed on the surface of the substrate.

FIG. 7D is a cross sectional view of the substrate after the secondmasks are removed. In this embodiment mode, a depth of digging in thefirst processing step is 48 μm and a depth of digging in the secondprocessing step is 110 μm. When the thickness of the substrate beforethe processing is 0.6 mm, the thickness of the substrate in the firstregion 203 becomes 0.6 mm, the thickness of the substrate in the secondregion 204 becomes 0.552 mm, and the thickness of the substrate in thethird region 205 becomes 0.442 mm. In this embodiment mode, the secondregion has the largest occupying area. The thickness of the substrate inthe second region is 0.552 mm, which is a preferable value for weightand thickness reduction of a display device. Of course, the thickness ofthe second substrate before the processing may be set to be 0.6 mm orless so that the weight of the display device can be further reduced.

Next, the amount of moisture which can be captured is estimated asfollows based on the amount of dry agent provided in the third region.Moisture permeability of the organic resin is 15 g/m² day to 30 g/m² dayin an environment of 60° C. and a humidity of 90%. In this embodimentmode, the moisture permeability of the adhesive is assumed to be 20 g/m²per day to estimate the amount of moisture which is transmitted throughthe adhesive and penetrated in the sealed region.

It is assumed that the display device of this embodiment mode has arectangular shape with a side of 7 cm and the height of the layer havingadhesion (adhesive) is 2 μm. An area of the layer having adhesionexposed to air is 0.56×10⁻⁶ m². When an exposed area is multiplied bythe moisture permeability, the amount of moisture transmitted per day isobtained as 114×10⁻⁷ g/day.

The total amount of moisture transmitted through the layer havingadhesion in 10 years is 41.6×10⁻³ g. When calcium oxide is used for thedry agent, the amount of calcium oxide required for absorbing 1 g ofmoisture is 3 g and the amount of calcium oxide for completely absorbingthe amount of moisture penetrating in 10 yours is 125 mg. Since thecalcium oxide is existent at 3.0 g/cm³, when a volume of the calciumoxide to be filled is 41.7 mm³, the total amount of moisture whichenters through the layer having adhesion in 10 years can be completedabsorbed.

The display region has a rectangular shape with a side of 60 mm andwidths of the driver circuit portion are 60 mm in a side parallel to thedisplay region and 3 mm in a side perpendicular to the display region.When three driver circuit portions (two gate drivers and one sourcedriver) are provided, an area occupied by the driver circuit portions is54 mm². In other words, when a gap is provided in a position of thesealing substrate corresponding to a region above the driver circuitportions and calcium oxide is filled therein, if the thickness of thedry agent made of calcium oxide is 77 μm, the volume of the dry agentbecomes 41.7 mm³. Thus, the amount of dry agent for completely absorbingthe amount of moisture entering through the layer having adhesion in 10years can be filled. In this embodiment mode, the thickness of the dryagent is 80 μm. Thus, it can be calculated that there exists the amountof dry agent sufficient for a long term usage (use for al least 10yours).

The amount of moisture transmitted through a seal member variesaccording to a temperature or humidity. Thus, the amount of dry agentused in the present invention may be determined as appropriate accordingto a use environment of the display device.

Embodiment Mode 2

In this embodiment mode, an example where a dry agent and a permeablefilm are provided over a driver circuit portion is indicated. In thisembodiment mode, points which are different from Embodiment Mode 1 willbe described in detail. This embodiment mode will be described using across sectional view of FIG. 2. FIG. 2 is a cross sectional view of anactive matrix display device using an active matrix organic lightemitting element. Shown in the drawing is a driver-circuit-integratedstructure in which a pixel portion 112 and a driver circuit portion 111are formed on the same substrate.

Substrates made of glass can be used as a first substrate 101 and asecond substrate 102.

In this embodiment mode, a granular material is used for a dry agent107. When the dry agent is granular, a surface area thereof is increasedand thus it is easier to absorb moisture. It is desirable that aparticle size of the dry agent is set to be 10 μm to 80 μm. In thisembodiment mode, the dry agent having the particle size of 30 μm isused. Also, in this embodiment mode, it is assumed that a third region105 in which the dry agent is provided is recessed by 100 μm relative toa second region 104. Calcium oxide is used for the dry agent.

In order to contain the dry agent in the third region 105, a permeablefilm which is composed of an adhesion layer 125, a porous layer 126, anda base member 127 is used. Polyester can be used for the base member anda polyfluoroethylene system fiber can be used for the porous layer.NTF1121 produced by Nitto Denko Corporation which has high moisturepermeability (moisture permeability of 6800 g/m²·24 hours in measurementbased on JIS K 7129 method A) is preferably used for the porous film.Also, the thickness of the permeable film is preferably 150 μm to 300μm. In this embodiment mode, the thickness of the permeable film is setto be 150 μm.

Also, a gap of about 50 μm is provided between the permeable film andthe driver circuit portion so that TFTs in the driver circuit portionare not in contact with the permeable film. Thus, considering thethickness of the permeable film (150 μm) and an interval between thepermeable film and the driver circuit portion, the second region 104 inwhich the permeable film is provided is recessed by 200 μm relative tothe first region 103.

It is desirable that the thickness of a layer 106 having adhesion forbonding the first substrate and the second substrate be as small aspossible. In this embodiment mode, the thickness of the layer havingadhesion is set to be 1.5 μm.

When a volume of the sealed space defined by the first substrate, thesecond substrate, and the layer having adhesion is to be decreased toreduce the total amount of moisture left in a dry gas in the sealedspace, a distance between the first substrate and the second substratein the pixel portion may be set to be shorter than a distance betweenthe first substrate and the second substrate in the driver circuitportion. Since there is no need to particularly provide the permeablefilm in the pixel portion, a distance between the substrates in thepixel portion can be arbitrarily determined in consideration of thevisibility of a display region and the like. In this embodiment mode,the distance between the first substrate and the second substrate in thepixel portion is set to be 50 μm.

In this embodiment mode, an anode 113, an organic compound layer 114,and a cathode 115 are laminated in this order to form an organic lightemitting element 116. A transparent electrode made of ITO is used as theanode. Alkali earth metal such as MgAg or alkali metal such as AlLi isused as metal having a small work function for the cathode. Thus, astructure in which light emitted from the organic light emitting elementis outputted from the first substrate 101 side is obtained. A holetransport layer, a light emitting layer, and an electron transport layerare laminated in this order to obtain the organic compound layer. Threekinds of light emitting layers corresponding to RGB are preferablyformed to enable color display.

When the thickness of the second substrate is set to be 0.7 mm, thethickness of the substrate in the first region becomes 0.7 mm, thethickness of the substrate in the second region becomes 0.5 mm, and thethickness of the substrate in the third region becomes 0.4 mm. In thesecond substrate, the second region has the largest occupying area.Thus, it may be considered that the thickness or the weight of thesecond substrate is substantially determined by the thickness of theglass substrate in the second region. In other words, the thickness ofthe glass substrate in the second region occupying the largest area ofthe substrate is 0.5 mm, which is a value suitable for reducingthickness and weight of the display device.

Also, with the structure according to this embodiment mode, the granulardry agent having a large surface area and high moisture absorption canbe provided in the sealed region using the permeable film. Also, in thisembodiment mode, the dry agent is provided on the driver circuitportion. However, the dry agent can also be provided above the pixelportion. Considering a direction of light emitted from the organic lightemitting element, even if the dry agent is provided on the pixelportion, it will not affect the display at all.

Embodiment Mode 3

This embodiment mode will be described using FIG. 3. As shown in FIG. 3,in a display device in which an organic light emitting element 116 isprovided, minute unevennesses are formed on the surface of a substrateonto which light emitted from the organic light emitting element isoutputted. Hereinafter, this embodiment mode will be described indetail.

In this embodiment mode, the organic light emitting element 116 has astructure in which a cathode 113, an organic compound layer 114, and ananode 115 are laminated in order, and light from the organic lightemitting element 116 is emitted to the side indicated by an arrow in thedrawing. In other words, a user views an image from a second substrate102 side. At this time, outside light is reflected at the interfacebetween the second substrate 102 and a sealed space and in an interfacebetween the second substrate and air. Thus, unwanted reflection of anambient background view is caused. In order to prevent such aphenomenon, minute unevennesses are formed on the surface of the secondsubstrate 102.

When the surface of the substrate is to be processed by an abrasivemachining method, a first region 103, a second region 104, and a thirdregion 105 are formed on the surface of the second substrate and then aparticle size of fine powder jetted onto the surface of the substrateand a jet speed thereof is controlled to form the minute unevennesses onthe surface of the first region, the second region, and the thirdregion. The heights of the minute unevennesses are set to be 0.1 μm to 3μm, preferably, 0.1 μm to 0.5 μm. In order to prevent diffraction, it ispreferable that the unevennesses having different curvatures areprovided to improve scattering property. Taking the spacing (pitch)between the convex portions as X, it is preferable to set X=0.05 to 1 μm(more preferably between 0.3 and 0.8 μm). In other words, by setting thepitch of the convex portions to be nearly equal to the wavelength ofvisible light, diffuse reflection (irregular reflection) of thereflected light can be made to occur effectively.

Also, in this embodiment mode, in order to prevent the reflection ofoutside light in an interface between the second substrate and air andthe resulting occurrence of unwanted reflection of an ambientbackground, an anti-reflective film 128 is formed in an interfacebetween the second substrate and air. In the case of a display devicecapable of performing color display, light having three colors of RGB isemitted. Thus, it is desirable that the anti-reflective film has areflectance of 1% or lower, preferably, 0.5% or lower over a wideband(400 nm to 700 nm).

According to this embodiment mode, reflection light produced in theinterface between the second substrate and the sealed space is scatteredby the minute unevennesses. Together with the effect of theanti-reflective film provided on the surface of the second substrate, anambient background of the second substrate is not reflected in theinterface of the second substrate to be recognized by a user.

EMBODIMENT Embodiment 1

The present invention can be applied to all display devices using anorganic light emitting element. FIG. 4 shows one example thereof, andshows an example of an active matrix display device manufactured usingTFTs. There is a case where the TFTs in this embodiment are divided intoan amorphous silicon TFT and a polysilicon TFT depending on a materialof a semiconductor film constituting channel forming region. However, ifa field effect mobility is sufficiently high, the present invention canbe applied to both TFTs.

An n-channel TFT 431 and a p-channel TFT 432 are formed in a drivercircuit portion 437. A switching TFT 433, a reset TFT 434, a currentcontrol TFT 436, and a storage capacitor 435 are formed in a pixelportion 438.

As a substrate 401, a substrate made of quartz or glass such as bariumborosilicate glass represented by #7059 glass, #1737 glass, and the likeproduced by Corning Corporation or aluminoborosilicate glass is used.

Then, a base film 402 made of an insulating film such as a silicon oxidefilm, a silicon nitride film, or a silicon oxynitride film is provided.For example, a silicon oxynitride film 402 a made from SiH₄, NH₃, andN₂O is formed at a thickness of 10 nm to 200 nm (preferably, 50 nm to100 nm) by a plasma CVD method. Similarly, a silicon oxynitride hydridefilm 402 b made from SiH₄ and N₂O is formed and laminated thereon at athickness of 50 nm to 200 nm (preferably, 100 nm to 150 nm). In thisembodiment, the base film 402 has a two layers structure. However, itmay also be formed as a single layer film of the insulating filmmentioned above or as a lamination of two or more of these layers.

Then, island-like semiconductor layers 403 to 407, a gate insulatingfilm 408, and gate electrodes 409 to 412 are formed. The thickness ofthe island-like semiconductor layers 403 to 407 is set to be 10 nm to150 nm, the thickness of the gate insulating film is set to be 50 to 200nm, and the thickness of the gate electrodes is set to be 50 nm to 800nm.

Then, an interlayer insulating film 413 having a laminate structure ofan insulating film made of an inorganic material such as silicon nitrideor silicon oxynitride and an insulating film made of an organic materialsuch as acrylic or polyimide is formed. The thickness of the interlayerinsulating film is preferably set to be 1 μm to 3 μm. It is desirablethat the insulating film made of the organic material has a thicknessenough to level unevenness in height caused by the island-likesemiconductor layers 403 to 407 and the gate electrodes 409 to 412.

Then, a cathode 423 of the organic light emitting element is formed. Amaterial such as MgAg or LiF is preferably used for the cathode. Thethickness of the cathode is preferably set to be 100 nm to 200 nm.

Then, a conductive film containing mainly aluminum is formed at athickness of 1 μm to 5 μm and etched. Thus, a data wiring 418, a drainside wiring 419, a power supply wiring 420, and a drain side electrode421 are formed in the pixel portion. The data wiring 418 is connectedwith the source side of the switching TFT 433. Although not shown, thedrain side wiring 419 which is connected with the drain side of theswitching TFT is connected with the gate electrode 411 of the currentcontrol TFT 436. The power supply wiring 420 is connected with the drainside of the current control TFT 436. The source side electrode 421 isconnected with the source side of the current control TFT 436 and thecathode. In the driver circuit portion 437, wirings 414 and 416 areconnected with the island-like semiconductor film 403 of the n-channelTFT 431, and wirings 415 and 417 are connected with the island-likesemiconductor film 404 of the p-channel TFT 432. Note that, in thisembodiment, a condition for etching the conductive film containingmainly aluminum is controlled to provide tapers having an angle of 15°to 70° relative to the surface (upper surface) of the interlayerinsulating film are provided in side surfaces of these wirings. Lightemitted from the organic light emitting element in random directions isreflected by these side surfaces of the wirings to thereby prevent totalreflection.

Then, a bank 422 made of an insulating material is formed so as to coverthese wirings. The bank 422 is formed so as to cover end portions of thecathode 423 so that a short circuit between the anode and the cathode inthis region is prevented. In this embodiment, a bank made of aninorganic material such as silicon oxide or silicon oxynitride is formedat a thickness of 1 μm to 3 μm. The inorganic insulating film is formedin parallel to taper surfaces of the drain side electrode 421 and thelike. Thus, the travelling direction of reflection light is easilyestimated based on Snell's law.

Then, an organic compound layer 424 of the organic light emittingelement is formed. The organic compound layer is used with a singlelayer or a laminate structure. However, when the laminate structure isused, higher light emission efficiency is obtained. Generally, a holeinjection layer, a hole transport layer, a light emitting layer, and anelectron transport layer are formed in this order on the anode. However,the organic compound layer may also has a structure such that a holetransport layer, a light emitting layer, and an electron transport layerare formed in this order or a structure such that a hole injectionlayer, a hole transport layer, a light emitting layer, an electrontransport layer, and an electron injection layer are formed in thestated order. In the present invention, any known structure may be used.

Note that in this embodiment, color display is performed by a method ofvapor-depositing three kinds of light emitting layers corresponding toRGB. As regards specific light emitting layers, preferably,cyanopolyphenylene is used for a light emitting layer for emitting lighthaving a red color, polyphenylenevinylene is used for a light emittinglayer for emitting light having a green color, and polyphenylenevinyleneor polyalkylphenylene is used for a light emitting layer for emittinglight having a blue color. The thickness of the light emitting layers ispreferably 30 nm to 150 nm. The above example is only one example ofmaterials which can be used for a light emitting layer, and thematerials are not limited to these.

Note that the organic compound layer indicated in this embodiment has alaminate structure of a light emitting layer and a hole injection layermade of PEDOT (polyethylene dioxythiophene) or PAni (polyaniline).

Then, an anode 425 made of ITO (indium tin oxide) is formed. Thus, theorganic light emitting element which is composed of the cathode made ofa material such as MgAg or LiF, the organic compound layer in which thelight emitting layer and the hole transport layer are laminated, and theanode made of ITO (indium tin oxide) is provided. Note that, when atransparent electrode is used as the anode, light can be emitted to asealing substrate (second substrate) 427 side in FIG. 4.

The outer edge portion of the sealing substrate 427 is convex to thefirst substrate. By this convex portion, a gap between the organic lightemitting element provided in the first substrate and the secondsubstrate in the pixel portion 438 is controlled. Since the gap isdetermined by means of the convex outer edge portion of the sealingsubstrate, the thickness of a layer 439 having adhesion, which isprovided between the sealing substrate and the element substrate can beminimized. In this embodiment, the thickness of the layer havingadhesion is set to be 1.0 μm.

Substrates made of glass are used for the sealing substrate and theelement substrate on which the organic light emitting element 426 isprovided. Note that, in this embodiment, the surface of the sealingsubstrate is processed to provide a dry agent 429 within a sealedregion. Thus, similar to the case where a metallic substrate is used asthe sealing substrate, moisture present in the sealed region can beabsorbed by the dry agent. The dry agent 429 is covered by a porous film430. The porous film is adhered to the dry agent by an adhesive 428.Also, the porous film is cut out in a circle, and an adhesive 440 isapplied to the thus exposed portion of the dry agent to thereby bond thedry agent onto the sealing substrate 427.

FIG. 5 is a top view of the pixel portion shown in FIG. 4 and referencenumerals common to those in FIG. 4 are used for convenience ofdescription. Note that, cross sections taken along lines A-A′ and B-B′in FIG. 5 are shown in FIG. 4. Further, the bank is provided outside theregions surrounded by chain lines. Also, the light emitting layerscorresponding to RGB are provided inside the regions surrounded by thechain lines.

FIG. 6 shows an equivalent circuit of such a pixel portion and referencenumerals common to those in FIG. 4 are used for convenience. Theswitching TFT 433 has a multi gate structure. LDDs overlapped with thegate electrode are provided in the current control TFT 436. Since a TFTusing polysilicon has a high operation speed, deterioration phenomenonsuch as a hot carrier injection is easy to occur. Thus, for manufactureof a display device having high reliability and capable of excellentimage display (having high operation performance), it is very effectiveto form TFTs having different structures (switching TFT in which an offcurrent is sufficiently low and current control TFT which is resistantto a hot carrier injection) in the pixel in accordance with a function.

Also, it is effective to provide a storage capacitor (condenser) 435 tohold the current control TFT 436 in an on state even after the switchingTFT 433 is changed from an on state to an off state, to thereby continuelight emission by the organic light emitting element and obtain displayat high luminance.

Further, in the case of a time divisional gradation system forperforming gradation display by changing a time interval of lightemission of the organic light emitting element, it is preferable thatthe reset TFT 434 is set to be an on state to change the organic lightemitting element from a light emission state to a non-light emissionstate to thereby control a time interval of light emission of theorganic light emitting element.

When the dry agent is provided near the organic light emitting elementin such a display device using the organic light emitting element, thedeterioration of the organic light emitting element can be prevented andthe stability of the display device can be ensured over a long period oftime. Also, since the gap can be controlled by using the sealingsubstrate, the thickness of the layer having adhesion, which is providedbetween the sealing substrate and the element substrate, can beminimized. Thus, the area of the layer having adhesion to be exposed tooutside air is decreased and thus the amount of water vapor transmittedthrough the layer having adhesion can be reduced.

Embodiment 2

In this embodiment, when mother substrates (mother glass) each having anarea equivalent to combined areas of a large number of unit panels arebonded to each other and then respective panels are to be severedtherefrom, a CO₂ laser is used as the severing means.

The CO₂ laser is a laser using carbon dioxide as a reactive medium andoperated in a population inversion state by causing carbon oxide to bein an excitation state. Since light having a wavelength of an infraredregion (10.6 nm) is generated by oscillation, an object to be irradiatedwith laser light can be heated.

A method of cutting a glass substrate by using a CO₂ laser will bedescribed using a perspective view of FIG. 9. FIG. 9 is a perspectiveview indicating a method of cutting one of glass substrates 501 and 502which are bonded together. An elliptic laser beam spot is irradiated byan optical system 504 for irradiating laser to the glass substrate 501moving in a direction indicated by an arrow and a coolant is blasted bya nozzle 507 onto a region (cooling region 506) behind the beam spot503. Thus, when the region heated by laser irradiation is rapidlycooled, thermal distortion is caused within the glass substrate so thatthe glass substrate 501 is severed along laser irradiation lines 505.

A laser scriber produced by Mitsuboshi Diamond Industrial Co., Ltd canbe used as an apparatus for cutting the glass substrate using the CO₂laser. Two mother substrates (mother glass) may be simultaneously cut ormay be cut one by one. It is preferable that two substrates aresimultaneously cut. This is because tact of the step is improved andthus productivity is increased.

When laser light from the CO₂ laser is irradiated to the surface of theglass substrate to cut it, generation of cutting scraps of the glasssubstrate is suppressed and a resulting operational failure can beprevented. In the method of cutting the substrate using the CO₂ laser,both laser irradiation and coolant blasting are performed in combinationso that a shock to the substrate is made small. Thus, when the shockresistance of the substrate is reduced due to the reduced thickness ofthe display device, the method of cutting the glass substrate using theCO₂ laser is effective.

Embodiment 3

The light emitting device manufactured by implementing the presentinvention is incorporated in various electronic appliances and the pixelportion is used as an image display unit. As an electronic appliance ofthe present invention, there are a mobile telephone, a PDA, anelectronic book device, a video camera, a notebook personal computer, animage reproduction apparatus provided with a recording medium such as aDVD (digital versatile disc) player or a digital camera. Specificexamples of these electronic devices are shown in FIGS. 10A to 10D andFIGS. 11A to 11C.

FIG. 10A shows a mobile telephone which is composed of a display panel9001, an operation panel 9002, and a connection portion 9003. A displaydevice 9004, a voice output unit 9005, an antenna 9009 and the like areprovided in the display panel 9001. Operation keys 9006, a power sourceswitch 9007, a voice input unit 9008, and the like are provided in theoperational panel 9002. The present invention can be applied to thedisplay device 9004.

FIG. 10B shows a mobile computer or a personal digital assistant, whichis composed of a main body 9201, a camera unit 9202, an image receivingunit 9203, an operational switch 9204, and a display device 9205. Thepresent invention can be applied to the display device 9205. A displaydevice of 3-inch to 5-inch size is used as such an electronic appliance.When the display device of the present invention is used, the weight ofsuch a personal digital assistant can be reduced.

FIG. 10C shows an electronic book device which is composed of a mainbody 9301, a display device 9303, a recording medium 9304, anoperational switch 9305, and an antenna 9306. This electronic bookdevice is used for displaying data stored in a mini disk (MD) or a DVDand data received by the antenna. The present invention is can beapplied to the display device 9303. A display device of 4-inch to12-inch size is used as the electronic book device. When the displaydevice of the present invention is used, reduction in weight andthickness of such an electronic book device can be realized.

FIG. 10D shows a video camera which is composed of a main body 9401, adisplay device 9402, a voice input unit 9403, an operation switch 9404,a battery 9405, and the like. The present invention can be applied tothe display device 9402.

FIG. 11A shows a personal computer which is composed of a main body9601, an image input unit 9602, a display device 9603, and a keyboard9604. The present invention is can be applied to the display device9603.

FIG. 11B shows a player using a recording medium in which a program isrecorded (hereinafter referred to as a recording medium), which iscomposed of a main body 9701, a display device 9702, a speaker unit9703, a recording medium 9704, and an operational switch 9705. Notethat, with this player, a DVD (digital versatile disc), a CD or the likeis used as the recording medium to play music, watch movies, play videogames or use the Internet. The present invention can be applied to thedisplay device 9702.

Also, in the operation of the mobile telephone shown in FIG. 10A, whendisplay brightness is increased while using the operation keys and thenthe brightness is lowered after the use of the operation keys isfinished, whereby power consumption can be reduced. Further, powerconsumption can be also reduced by increasing the display brightnessupon receiving an incoming call and then lowering it during a telephoneconversation. Furthermore, power consumption can be also reduced byproving a function such that display is turned off based on time controlunless reset operation is performed during continuous use of thetelephone. Note that these operations may be made by manual control.

Although not shown here, the present invention can be also applied to adisplay device incorporated in a navigation system, a refrigerator, awasher, a microwave oven, a fixed telephone, a facsimile, or the like.Thus, an application range of the present invention is extremely wide sothat the present invention can be applied to various products.

As described above, when the present invention is used, the gap can becontrolled by the convex portion of the sealing substrate and thethickness of the layer having adhesion provided between the sealingsubstrate and the element substrate can be minimized. Thus, the area ofthe organic resin material (having adhesion) exposed to outside air inthe side surfaces of the display device is decreased. Accordingly, theamount of moisture which is transmitted through the organic resinmaterial and penetrated in the sealed region, which is obtained as theproduct of the area to be exposed to outside air and moisturepermeability can be reduced.

Conventionally, in order to provide a dry agent in the sealed region, itis necessary to bond a metallic sealing substrate and a glass substratetogether. Thus, when the shock resistance of the glass substrate isreduced due to its reduced thickness, because of a difference in thermalexpansion coefficient between metal and glass, there is a possibilitythat a distortion is caused by rapid thermal change and the glasssubstrate is damaged as a result. However, according to the presentinvention, the sealing substrate and the element substrate can be madeof the same material so that the resistance to a thermal shock isimproved. Also, since the surface of the glass substrate is processedand the dry agent is provided, as in the conventional art, moisture isabsorbed by the dry agent. Thus, reduction in light emission intensitydue to moisture, occurrence of a dark spot, reduction of a lightemission area due to enlarged dark spot, and deterioration of theelement can be suppressed.

1. (canceled)
 2. A light emitting device comprising: a first substrate;a light emitting element comprising a light emitting layer comprising anorganic compound over the first substrate; and a second substrate overthe light emitting element, the second substrate bonded to the firstsubstrate through a layer having adhesion, wherein the second substratecomprises a first region overlapped with the layer having adhesion and asecond region overlapped with the light emitting element, wherein eachof the first region and the second region comprises minute unevennesseson a bottom surface of the second substrate, and wherein the minuteunevennesses in the first region are in contact with the layer havingadhesion.
 3. The light emitting device according to claim 2, whereineach of the first substrate and the second substrate is a glasssubstrate.
 4. The light emitting device according to claim 2, whereinheights of the minute unevennesses in the first region are set to be 0.1μm to 3 μm.
 5. The light emitting device according to claim 2, whereinthe layer having adhesion comprises an ultraviolet light curable resinor a heat curable resin.
 6. The light emitting device according to claim2, wherein a thickness of the layer having adhesion is 10 μm or less. 7.The light emitting device according to claim 2, wherein light emittedfrom the light emitting element enters the second substrate from thebottom surface of the second substrate, and wherein the light emittedfrom the light emitting element is released from a top surface of thesecond substrate through the second region.
 8. An electronic appliancecomprising a display device comprising the light emitting deviceaccording to claim 2 in a display portion.
 9. A light emitting devicecomprising: a first substrate; a light emitting element comprising alight emitting layer comprising an organic compound over the firstsubstrate; and a second substrate over the light emitting element, thesecond substrate bonded to the first substrate through a layer havingadhesion, wherein the second substrate comprises a first regionoverlapped with the layer having adhesion, a second region overlappedwith the light emitting element, and a third region overlapped with adriver circuit, wherein each of the first region, the second region, andthe third region comprises minute unevennesses on a bottom surface ofthe second substrate, wherein a dry agent is provided in the thirdregion, and wherein the minute unevennesses in the first region are incontact with the layer having adhesion.
 10. The light emitting deviceaccording to claim 9, wherein each of the first substrate and the secondsubstrate is a glass substrate.
 11. The light emitting device accordingto claim 9, wherein heights of the minute unevennesses in the firstregion are set to be 0.1 μm to 3 μm.
 12. The light emitting deviceaccording to claim 9, wherein the layer having adhesion comprises anultraviolet light curable resin or a heat curable resin.
 13. The lightemitting device according to claim 9, wherein a thickness of the layerhaving adhesion is 10 μm or less.
 14. The light emitting deviceaccording to claim 9, wherein light emitted from the light emittingelement enters the second substrate from the bottom surface of thesecond substrate, and wherein the light emitted from the light emittingelement is released from a top surface of the second substrate throughthe second region.
 15. An electronic appliance comprising a displaydevice comprising the light emitting device according to claim 9 in adisplay portion.
 16. A light emitting device comprising: a firstsubstrate; a light emitting element comprising a light emitting layercomprising an organic compound over the first substrate; and a secondsubstrate over the light emitting element, the second substrate bondedto the first substrate through a layer having adhesion, wherein thesecond substrate comprises a first region overlapped with the layerhaving adhesion and a second region overlapped with the light emittingelement, wherein the first region comprises minute unevennesses on abottom surface of the second substrate, and wherein the minuteunevennesses in the first region are in contact with the layer havingadhesion.
 17. The light emitting device according to claim 16, whereineach of the first substrate and the second substrate is a glasssubstrate.
 18. The light emitting device according to claim 16, whereinheights of the minute unevennesses in the first region are set to be 0.1μm to 3 μm.
 19. The light emitting device according to claim 16, whereinthe layer having adhesion comprises an ultraviolet light curable resinor a heat curable resin.
 20. The light emitting device according toclaim 16, wherein a thickness of the layer having adhesion is 10 μm orless.
 21. The light emitting device according to claim 16, wherein lightemitted from the light emitting element enters the second substrate fromthe bottom surface of the second substrate, and wherein the lightemitted from the light emitting element is released from a top surfaceof the second substrate through the second region.
 22. An electronicappliance comprising a display device comprising the light emittingdevice according to claim 16 in a display portion.